An electrophotographic toner, so-called an electrostatic toner (hereinafter, also called “toner”), is used, in an electrostatic electrophotography, in order to develop a latent image formed by electrification and exposure to form a visible image. The electrostatic toner is an electrically-charged fine powder prepared by dispersing a colorant such as carbon black and a pigment in a resin. Electrostatic toners are roughly classified into a dry-type two-component toner, in which the toner is used together with a carrier such as iron powders and glass particles; a wet-type toner, which is a dispersion system prepared by using an organic solvent such as an isoparaffin; and a dry-type one-component toner, in which a magnetic fine powder is dispersed.
An image obtained by being developed on a photoreceptor by using an electrostatic toner is transferred on paper, and an image directly developed on paper on which a photosensitive layer is formed is directly fixed by means of heat or solvent vapor. In particular, fixing using a heating roller, which is a contact-type fixing method, is advantageous in terms of e.g. having high thermal efficiency, ensuring image-fixing even with a relatively low temperature heating source and being suited for high-speed copying.
However, the image-fixing by contacting a heating element such as a heating roller with an electrophotographic toner may involve part of the toner being adhered on the surface of the roller and transferred on a subsequent image part: so-called offset phenomenon. A method that is proposed in order to solve this problem is adding a nonpolar wax such as a low-molecular-weight polyethylene wax or low-molecular-weight polypropylene wax to impart releasability to the toner.
A method that is proposed to improve offset resistance is, for example, using, as a wax, a propylene/1-butene random copolymer wax (Patent Document 1). It is described in this document that said method achieves excellent releasability, low heat fixing temperature and almost no occurrence of offset even in high-speed copying.
However, according to the study by the present inventors, it has been found that the above-described developer still needs improvements in terms of its ability to be fixed when a relatively-low-temperature heating element is used (low-temperature fixability) and absence of problems such as occurrence of stickiness of the toner after stored (toner storage property). Regarding the latter-mentioned property, it has been found that heat-curing of the toner may involve blocking of the wax itself, resulting in decrease of handling property and that in the application of the toner to additives such as a toner releasing agent, final products may undergo blocking.